Background Keloidal basal cell carcinoma (BCC) has been reported as a rare but distinctive variant of BCC.
Objectives To determine the frequency of keloidal collagen in BCC and to correlate it with clinical, histopathological and immunohistochemical features.
Methods Over 12 months, all cases of BCC with thick sclerotic collagen were collected and studied for clinical diagnosis, site, histopathological features and immunohistochemistry (collagen I, III, IV, laminine) in comparison with five keloids.
Results Of 1011 BCCs seen, 18 showed thick sclerotic collagen. In two cases, these stained positive for collagen type IV or laminine, indicating basement membrane material. In 16 cases, sclerotic bundles stained positive for collagen type I but not for types III, IV, and laminine, as do keloids. The clinical diagnosis was BCC (13), squamous cell carcinoma (one) or keloid (one). Fourteen lesions came from the face, nine of them from the ear. Keloidal collagen was extensive in 10 lesions, including all from the ear. Histologically, tumours often had morphoeiform zones (14), necrosis en masse (eight) and ulceration (nine).
Conclusions Keloidal collagen in BCC is not as rare as reported and consists of type I collagen, the same as in keloids. It does not characterize a distinctive clinicopathological entity but is found in different histological types of BCC with varying clinical appearance. Keloidal collagen in BCC is associated with morphoeiform features, ulceration and necrosis. Interestingly, extensive keloidal collagen is more often seen in BCC on the ear, a site prone to develop keloids.